Seismic surface waves and borehole methods to determine shear wave velocity: A review of measurement practice by contractors in the UK

In high-speed railways if the soil surface wave velocity approaches the train speed this can cause dynamic issues with the track. For the new high-speed railway (HS2) in the UK, Rayleigh and shear wave velocities (Vs) are determined as part of construction compliance testing using seismic surface waves methods (typically Multichannel Analysis of Surface Waves (MASW) and Continuous Surface Waves (CSW)). However, as these methods are not standardised, there is the potential for differences in how contractors design, collect and process test data which could lead to differences in assessment for any given site. As part of a wider project investigating such tests, a qualitative interview study was undertaken of contractors testing HS2 earthworks to understand how they design and undertake such investigations. The interviews focus on data capture, data processing and interpretation of seismic surface waves methods, but are also compared to the methods used of measuring Vs in boreholes. This show there is variation in testing and analysis protocols for similar sites and experience is important in undertaking such work. Contractors use experience from other projects and review their processes on site to check the data is suitable. They use both commercial and inhouse software for data analysis and the final velocity profiles produced strongly depend on the assumptions made around soil conditions. While there are many similarities in approach used, the differences lead to variability in results. The paper concludes by proposing elements of the testing that could (with further work) be included in best practice guidance around data collection and processing.